The operation of some power plant systems, for example certain simple-cycle and combined-cycle power plant systems, include the use of gas turbines. The operation of a gas turbine includes the use of pressurized gas flows at extreme temperatures traveling through flowpaths of the gas turbine, these pressurized gas flows driving a rotor of the turbine (e.g., power generation). Exposure of some components of the gas turbine (e.g., those not in the flowpath, wheel spaces, etc.) to these pressurized gas flows may reduce system/component lifespan and decrease system efficiency. As a result, interfaces between the flowpath and other portions of the gas turbine may include tight clearances which limit leakage/ingestion of hot gases (e.g., back flow) throughout the gas turbine.
In some systems, a purge flow may be introduced to one side of these interfaces to control leakage between the flowpath and other portions of the gas turbine (e.g., rotor back flow margin, wheel space back flow margin, etc.) by creating a targeted pressure ratio across the interface. This purge flow increases a pressure on one side of the interface relative to the other side, creating the targeted pressure ratio such that gas flow will only travel from the high pressure side to the low pressure side. However, as it is difficult to obtain rotating pressure measurements of the gas turbine during operation, and gas turbines operate across a wide range of external and internal conditions (e.g., temperatures, speeds, pressures, etc.), these systems may be limited to open looped control of the purge flow supply. This open-looped control operating substantially blind to operating conditions (e.g., environmental factors, cold-day performance, etc.), and requiring a maximum (e.g., worst-case scenario) amount of purge flow to be supplied to the gas turbine at all times to insure that the necessary pressure gradient exists across the interface. As such, purge flow requirements may be conservative resulting in losses in system efficiency and a demand for purge flow which is greater than necessary.